Apparatus for distributing textile flock on a web



June 15, EW NG ET APPARATUS FOR DISTRIBUTING TEXTILE FLOCK ON A WEB Filed May 3, 1949 /N VE N TORLS HEW/N6 TS'8MCKMOJE @wwu A TTORNEXS' Patented June 15, 1954 UITE TTES FAT NT QFFlCE APPARATUS FGR DISTRIBUTING TEXTILE FLOCK ON A WEB tion of Delaware Application May 3, 1949, Serial No. 91,092

Claims priority, application Great Britain May 5, 1948 4 Claims.

This invention relates to the distribution and fixation of fibres and other particulate material on an adhesive surface, and has as its principal object to provide a simple and inexpensive process and apparatus for distributing staple fibre substantially uniformly over a moving adhesive surface (e. g. an adhesive coated surface of a moving textile fabric) with the fibres aligned so that their axes are perpendicular to said surface, and fixing the fibres to the fabric by means of the adhesive so as to prvide the fabric with a pile or a suede finish.

U. 5. Patent No. 2,557,327 of September 11, 1951 describes the production of pile fabrics of the kind in which the pile is of staple fibre bonded to a backing fabric, by a method in which the fabric is first provided with a sticky coating of a thermoplastic polymer and a mixture of two plasticisers therefor of substantially different volatilities, the staple fibre is then applied to this coating so as to adhere thereto, and the coated fabric is heated to cause preferential evaporation of the more volatile plasticiser and conversion of the sticky coating into a non-' sticky flexible coating. The method specifically described for applying the staple fibre to the coated fabric is to sift the fibre on to the coated fabric and distribute it thereon by means of a beater. The present invention provides inter alia an improved method of applying the staple fibre in the production of pile fabrics by the general method referred to, i. e. by bonding a staple fibre on to a coated backing fabric.

The process of the present invention comprises causing said surface to pass between an earthed metallic surface and an unearthed metallic surface, feeding the particulate material between the adhesive surface and the unearthed surface, alternately charging and discharging said unearthed surface through a variable spark gap in such a way as to establish between said metallic surfaces and perpendicular to said adhesive surface, an alternating field in which, during each cycle, the intensity rises steeply to a maximum from which it falls steeply, continues for a longer period than that occupied by said rise and fall at substantially zero intensity, falls steeply to a minimum arithlnetically equal to said maximum and rises steeply therefrom, controlling the characteristics of said field by the size of the spark gap so that particles of the said material move rapidly back and forth between the unearthed surface and the adhesive surface until they become embedded in the latter, and hardening the adhesive surface to fix the particles.

In its application to the production of pile fabrics, the invention comprises a process of the kind defined in the preceding paragraph in which the particulate material is a flock of textile fibre the surface on which the fibre is distributed and fixed is that of an adhesive coating on a textile fabric. The effect of the field established in the condenser through which the fabric passes is to set the fibre in motion and produce on said surface a substantially uniform distribution of fibres, the fibres being aligned with their axes substantially perpendicular to said surface, and adhering thereto. The fabric then passes from the condenser into a region wherein the adhesive is hardened, so permanently anchoring the pile.

Apparatus suitable for carrying out the process of the invention comprises an electrostatic plate condenser having one plate earthed and the other unearthed and connected through a variable spark gap to a high-tension magneto, means for moving the adhesive surface through said condenser perpendicular to the field established therein by operation of the magneto, means for feeding the particulate material between the unearthed plate and the adhesive surface, and means for hardening the adhesive after passage through the condenser.

Apparatus for forming pile fabrics by the process of the invention includes a flock-distributor which may, for instance, comprise a hopper feeding on to an oscillating screen, or a rotating cylinder with perforated sides, or a hopper feeding the flock by means of a paddle through a screen, placed so as to feed the flock into the vicinity of the adhesive surface near where the fabric enters the condenser, a heating chamber for setting the adhesive after the fabric leaves the condenser, means for drawing the fabric past the flock-distributor through the condenser and heating chamber, and means for taking up the pile fabric formed. The apparatus should be so constructed that neither the adhesive coated surface nor the pile come into contact with surfaces that might damage them. To this end, in the preferred form of apparatus all guide rolls contact only the uncoated or back surface of the fabric, and the necessary traction is applied by pin-rolls.

It will be observed that the electrical apparatus of the invention, unlike other electrical apparatus that has been proposed for electro-coating, is very simple, cheap, and readily available since, as the source of current, all that is required is a magneto which may be of a standard type used for automobile or aircraft engines. By the combination of the magneto with a spark gap of suitable width in series, the very sharp rise and fall of intensity in the field at each alternation, the dwell at substantially zero intensity, the equally sharp reverse fall to and rise from a minimum arithmetically equal to the maximum, the magnitudes of maximum and minimum, and the frequency, which we find best adapted to orient the fibres or other particles and impel them on to the adhesive surface, are readily obtained at a very small expenditure of power, and since the current generated is so small, danger to the operatives is minimised. The adjustable spark gap enables the best field-characteristics for a particular combination of particulate material and fabric or other backing material, under particular atmospheric conditions, to be quickly obtained.

The best results have been obtained when, in addition to the variable spark a fixed spark is provided between the secondary winding of the magneto and the variable gap. This fixed gap may, for instance, be provided by feeding the current in the secondary to the distributor terminals through a rotating arm between which and the several terminals at its nearest approach to them there is a of several millimetres. The variable gap will in general need to be set much wider than the fixed gap, e. g. 6 to 12 mm.

It is of great advantage to provide between the earthed plate of the condenser and the path of the fabric a sheet of material of dielectric constant at least 3 and. preferably higher, e. g. polyvinyl chloride, or rubber hydrochloride. This increases the charge which the condenser can take without discharge between the charged plates and the earthed plate. The magneto should be capable of charging the condenser to at least 10,000 volts, and preferably to a considerably higher voltage, e. g. up to 50,000 volts or even up to 100,000 volts. In general the greater the distance apart of the plates the higher the voltage should be. With the condenser plates at a distance apart of A to 1 inch, e. g. inch, useful results have been obtained with voltages between 20,000 and 50,000, e. g. 0,000. A suitable range of frequency for the alternating field is 10 to 80 and especially 10 to 20 cycles per secout]. In general, the greater the distance between the plates the lower should be the frequency of interruption.

In carrying out the invention, excellent results have been obtained using as the backin -fabric a fabric of cotton or other form of cellulose, including regenerated cellulose. Fabrics of high tenacity regenerated cellulose such as is obtainable by saponifying cellulose acetate yarn that has been stretched considerably in steam or hot water are particularly suitable when a strong light-weight backing fabric is required. Backing fabrics of other materials can be used, including materials of higher dielectric constant and dielectric strength and lower moisture regain, than cotton, for example silk, wool, casein, soya-bean protein and other proteinaceous fibers; cellulose esters and ethers; fibre forming condensation polymers such as nylon; fibre-forming addition polymers such as co-polymers of vinyl chloride with vinyl acetate, with vinylidene chloride, or with acrylonitrile, or of acrylonitrile with methacrylonitrile; and mineral fibre-forming materials such as glass.

The staple fibre used. may be composed of any of the materials specified above with reference to the backing fabric. Excellent products have been 4 obtained with staple fibre of length between 1 and 4 mm.

The adhesive used may be of the kind referred to in U. S. Patent No. 2,507,327. Thus, for ex ample, a suitable adhesive comprises polyvinyl acetate plasticised with a major proportion of a I volatile plasticiser such as dimethyl phthalate,

glycol diacetate, triethyl phosphate or tributyl phosphate, and a minor proportion of a less volatile plasticiser such as tricresyl phosphate or triphenyl phosphate. As described in the said application, a thin foundationdayer of plasticised l cillOl'lde is preferably provided for Such an a 'lhesive. Another form of adhesive that is very suitable, particularly for bonding cellulose acetate fibre to a cellulose acetate fabric, comprises a solution in a volatile solvent of a copolyof butadiene and acrylonitrile, vulcanising ingredients therefor, and mixture of two plasticisers of different volatilities. e. dimethyl phthalate and dibutyl phthalate or tricresyl phosphate. The solution is applied to the fabric, the volatile fabric evaporated leaving a sticky coating and, after formation of the pile, the coating is hardened by evaporation of more volatile plasticiser and vulcanisation of the polymer. Other kinds of adhesive capable of being hardened to give a flexible coating, so firmly anchoring the pile, can be used. Thus, for example, the adhesive may be a dispersion of a polymer such as polyvinyl chloride, that undergoes gelling when heated. Blends of polyvinyl chloride or the like with rubber-like polymers, e. g. co--polymers of butadiene with acrylonitrile, may also be used. Or the adhesive may have a basis of a heathardening synthetic resin, e. g. a heat-hardening addition polymer such diallyl phthalate or allyl diglycol phthalate, any necessary catalyst being present in the adhesive composition. Ad hesives having a basis of an aqueous emulsion such as rubber latex which can be set by drying can also be used.

The hardening of the adhesive coating after application of the staple-fibre may be effected, for example, by radiant heat, by dielectric heating, or by means of a current of hot air.

The accompanying diagrammatic drawing shows by way of example, in part-sectional elevation, a lay-out comprising a form of apparatus according to the invention.

The fabric l is drawn from the supply roll 2 over supporting roll 3 and guide bars l under the dope-casting box 5 and doctor-blade 6, to the heating cabinet 7. Dope comprising a heathardenable adhesive in solution in volatile solvent is supplied to the dope-casting box 5 by the pump 5a and forms a thick layer is on the fabric I, this layer being spread by the doctor-blade 6 to form a thin even layer lb. Within the dryer 1 the fabric is heated by infra-red heaters 0; air is drawn in through apertures 9 and air and solvent vapours are drawn off through the duct iii to solvent recovery plant not shown.

From the heating cabinet '3 the fabric passes beneath a flock-distributor l I comprising a hopper I2 feeding on to a screen l3 which is oscillated by spring-cam mechanism i to distribute fiock E0 on to the adhesive layer lb of the travelling fabric.

The fabric passes over guide roll it: and through the electrostatic condenser I0. The condenser comprises a single earthed plate ll covered on the inside with a dielectric layer Ila of polyvinyl chloride sheet, and three plates i8, I9 and 20 connected through variable spark gaps 2 i, 22 and 23 respectively to the collecting leads 24, 25 and 26 respectively. The collecting lead 24 is connected to the terminals 21, 30 and 33 of the distributor 36 of the 4-pole, 9-point high-tension magneto 31. Similarly, the collecting lead 25 is connected to the terminals 35, 29 and 32, and the collecting lead 26 to the terminals 34, 28 and 3|, of the distributor 36.

The distributor has a rotating arm 36a which distributes current generated in the secondary of the magneto to each of the terminals 21 to 36 in turn. The rotating arm does not make contact with the terminals but clears them by several millimetres, thus providing an additional spark gap of fixed dimensions between the secondary of the magneto and the adjustable spark p.

On driving the magneto 31, each of the plates l8, I9, 20 receives alternately a high positive followed by a high negative charge. The characteristics of the field so produced in the condenser lfi are adjusted by adjustment of the spark gaps 2!, 22 and 23 until the individual fibres of the flock lc align themselves perpendicular to the plates l8, l9 and 20, and substantially equidistant from one another, and move rapidly back and forth between those plates and the adhesive coating lb of the fabric I. In the course of their movement away from the plates l8, l9 and 20, the fibres become stuck at one end to the adhesive layer lb, so forming a pile id on the fabric. The condenser and the run of the fabric therethrough can be horizontal, but better distribution of flock is obtained with the vertical arrangement illustrated.

From the condenser the fabric passes over a guide-roll 33 and past a revolving brush 39 which lays the pile, into a stentor-type heater 40. During passage through this heater the adhesive in the layer lb is hardened, so firmly anchoring the pile. From the heater the fabric is removed by a pin-roll 4| and collected in folds 42 by a plaiter (not shown).

Using a 4-pole, 9-point Watford aero-magneto, the connections shown give a frequency of 11 cycles per second at 1,000 revolutions per minute. At this speed, and with the three unearthed condenser plates shown having each an area of 38 x 12 inches and inch apart, and with a fixed spark gap of 2 mm., adjustment of the variable spark gap within the range to 15 mm. will give suitable activation of a flock of cellulose acetate, cotton, regenerated cellulose or silk.

Other types of magneto, e. g. 2-pole, 4- or 6- point magnetos, connected in such a way and driven at such a speed as to give comparable output and frequency can be used. The fixed spark gap may be dispensed with or reduced to negligible dimensions as in the usual rotating arm type of distributor, but at some sacrifice of efficiency. Elimination of both fixed and variable spark gaps has been found to lead to complete failure to distribute and impel the flock on to the adhesive surface. Introduction of one or more further spark gaps in series increases the activation of the flock but also makes satisfactory adjustment difiicult.

The following examples illustrate the invention:

Example 1 The apparatus used was that described above with reference to the drawing.

A cellulose acetate woven fabric was run through the machine at a speed of 2 yards per minute.

From the dope-casting box 5 there was spread on the fabric a dope of the following composition, all the parts being by weight:

150 parts of Hycar O. R. 25 (a rubber-like copolymer of butadiene and acrylonitrile) 3 parts of sulphur 3 parts of a 4:1 mixture of mercapto-benz-thiazole and diphenyl guanidine 7.5 parts of zinc oxide 37.5 parts of a cumarone resin of melting point 300 parts of dimethyl phthalate 4.5 parts of di-octyl phthalate 378 parts of methyl ethyl ketone 252 parts of methyl isobutyl ketone 3 parts of pigment The dope was applied at the rate of 3 /2 oz. per square yard.

The condenser plates were inch apart; the fixed spark gap between the rotating arm of the distributor and the output terminals thereof was 2 mm.; the magneto, a e-pole, 9-point Watford type, was run at 1,000 revolutions per minute.

The flock used was a cellulose acetate fibre ground to a length of 1 mm. and coloured to match the pigment in the dope.

After passage under the doctor-blade 6, the volatile solvent was evaporated from the coating of dope, leaving a sticky coating, during passage of the fabric through the heating cabinet "I which was maintained at to C., the time of passage through the heating cabinet being 1 minute.

The adjustable spark gaps 2|, 22 and 23, in which the terminals across which the sparking occurred were plates 4 mm. in diameter, were adjusted to give maximum to-and-fro movement of the flock. Under the atmospheric conditions prevailing the correct adjustment was found to be 12 mm.

Passage through the condenser caused flock to adhere to the sticky coating, the fibres being upstanding and substantially equidistant from one another, and forming the desired pile. The pile was brushed by the rotating brush 39 to lay the pile and remove any loose fibres.

The fabric then passed through the stentortype heater 40 where, during an exposure of 15 minutes at about 130 C., the adhesive was hardened by evaporation of dimethyl phthalate and vulcanisation of the rubber-like polymer.

Example 2 The process was carried out as in Example 1 except that the dope used had the following composition (all the parts being by weight) 150 parts of polyvinyl acetate parts of dimethyl phthalate 30 parts of tricresyl phosphate 750 parts of acetone 3 parts of pigment the backing fabric was of regenerated cellulose fibre of tenacity 6 guns. per denier; the evaporation of acetone was carried out at 50 C., and the final heating to evaporate dimethyl phthalate, at 150 C.

Example 3 The process was carried out as in Example 2 but substituting triethyl phosphate for dimethyl phthalate and evaporating this plasticiser at C.

temper Instead of the cellulose acetate fibre, fibre of cotton, regenerated cellulose or natural silk of fibre length 1 to 3 mm. can be used with appropriate adjustment of the variablespark gap.

It will be notedthat the adhesive passing through the condenser is substantially free from inflammable solvent volatile enough to present a fire-hazard through sparking. Another way of avoiding this hazard is to formulate the cement, for instance a cement having a basis of a rubber-like polymer, with a volatile noninflammable solvent such as a chlorinated lower aliphatic hydrocarbon. In this case, the pielllrii nary evaporation of solvent can be'stopped short while the coating is still sticky, hardening may be effected by completing the evaporation after formation of the pile, the more volatile plasticiser being omitted, but special care must be taken to avoid poisoning of the operatives by exposure to the solvent vapours, and it is preferred to avoid the use of such toxic solvents. In the methods illustrated in the examples, there is no danger of toxic concentrations of vapour being developed while the fabric is passing through the condenser, and this part of the apparatus need not,

therefore, be enclosed, but adequate provision should be made for removal of the vapours of solvent and more volatile plasticiser during evaporation of these liquids, i. e. in the two heating steps.

By duplicating the condenser and magneto and spark gap unit shown in the drawing, the speed at which the fabric can be run through the apparatus can be increased.

The invention has been described with special reference to the manufacture of pile fabrics. The method and apparatus or" the invention, however, are capable of other applications where it is desired to distribute and fix particulate material on a moving adhesive surface, such as that of a suitably coated textile fabric. Thus, for example, pigments, metallic powders and other effect materials may, by the process and apparatus of the invention, be distributed and fixed on adhesive surfaces of fabrics, films, paper and other webs, provided that the particles used are sufiiciently light in weight to show the desired movement under the influence of the field provided.

Having described our invention, what we desire to secure by Letters Patent is:

1. In apparatus for causing fibers of a textile flock, under the influence of an electric field, to become distributed over and anchored to an adhesive-coated web passing through said field, the combination of a plate condenser having an air space between the plates, means for guiding a' web through said air space and parallelto the plates of said plate condenser, an adjustable spark-gap, and a generator of periodically varing high-tension electromotive force, said gener'ator being such that the electroznotive force during each cycle, rises steeply to a peak, immediately falls steeply therefrom, remains substantially zero for a much longer period than that occupied by said rise and fall, falls steeply to a minimum arithmetically equal to said peak, immediately rises steeply therefrom, and continues at substantially zero for the remainder of the cycle, one plate of said condenser being connected through the spark-gap to one out put terminal of said source and the other plate being connected to the other output terminal of said source.

2. In apparatus for causing fibers of a textile flock, under the influence of an electric field, to become distributed over and anchored to an adhesive-coated web passing through said held. the combination of a plate condenser having an air space between the plates, means -for guiding a web through said air space and parallel to the plates of said plate condenser, an adjustable spark-gap, a high-tension magneto and means for driving said magneto, one plate of said condenser being connected through the spark-gap to a live terminal of the magneto and the other plate being connected to the grounded terminal of the magneto.

3. Apparatus according to claim 2, wherein a fixed spark-gap is in series with the adjustable spark-gap.

4. Apparatus according to claim 2, comprising within the condenser, adjacent to one plate thereof, and coextensive with said plate, a sheet of material of dielectric constant at least 3.

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